Pulse and square wave generator



Jan. 18, 1949.

J. D. SCHANTZ PULSE AND SQUARE WAVE GENERATOR Filed Aug. 26, 1944 l 4 I 7 2 OUTPUT SIGNAL l3 l4 f IS 2s INVENTOR Patented Jan. 18, 1949 PULSE AND SQUARE WAVE GENERATOR Joseph D. Schantz, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application August 26, 1944, Serial No. 551,320

This invention relates to square wave generators and particularly to pulse and square wave generators utilizin a multivibrator circuit.

A multivibrator is an oscillator comprising two thermionic tubes having their plates cross-conneoted by condensers to their grids. In other words, the plate of each tube is capacity coupled to the grid of the other tube. A multivibrator can be arranged to oscillate at a natural frequency which is determined by the value of the coupling condensers and their grid'leak resistors, through which the condensers discharge.

However, a multivibrator can also be arranged so that it is not self-oscillating and requires driving impulses from an external source which determine the frequency of the output signal.

Multivibrators have been used in the past for generatin square waves which find wide application in the television and related fields. They are used, for instance, for deriving square wave 4 voltages which may be employed for timing the scanning beams of television pickup and receiving tubes.

The demands made with regard to the constancy and stability of the current or the voltage wave shape are extremely severe particularly where the square wave is used for timing the line scanning of a television pickup or receiving tube. Prior multivibrator circuits devised for this purpose do not generate a square Wave form hav ing suificiently steep leading and trailing edges to satisfy these demands. Consequently prior art generators require additional circuit means to provide the desired wave shape.

It is an object of the present invention, therefore, to provide a novel multivibrator circuit for generating square wave impulses having steeper leading and trailing edges than obtainable heretofore.

Another object of this invention is to provide a self-oscillating multivibrator circuit for generating an output signal at a harmonic of the frequency of the driving or synchronizing input pulses.

In accordance with the present invention there is provided a square wave generator comprising a multivibrator including two electric discharge tubes each having a cathode, a grid and an anode. Condensers are provided for coupling the anode of each tube to the grid of the other tube, and a potential is supplied to the anodes of the two ,tubes that is positive with respect to ground.

The grid of the first tube is connected to ground through a grid leak resistor, and the'cathode of the second tube is connected to ground through 13 Claims. ((31. 250-36) 2 another resistor. Hence, the first tube circuit has a predetermined time constant which is determined by the condenser coupling its grid to the anode of the second tube and by its grid leak resistor. The second tube does not have a grid leak resistor and, therefore, the external circuit connected to the grid of the second tube has an infinite time constant. This multivibrator is not self-oscillating and must be driven from a foreign source. To this end means are provided for supplying an input signal to themultivibrator and for deriving a square wave output signal from the second tube.

In accordance with another embodiment of the invention there is provided aresistor for connecting the cathode of the first tube to ground. By

I means of this. cathode resistor the multivibrator is made self-oscillating while the input signal insures synchronization of the oscillations. The output signal is, therefore, obtained at a harmonic of the fundamental frequency of the input signal.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. I

In the accompanying drawing, Fig. 1 is a schematic diagram of a multivibrator in accordance with the invention arranged for generating sharp square wave impulses, While Fig. 2 is a schematic circuit diagram of a modified form of multivibrator arranged for generating square wave impulses at a multiplied frequency.

Referring now more particularly to Fig. 1, there is provided a multivibrator comprising two thermionic tubes I and 2. The thermionic tubes l and 2 are enclosed in a common envelope 3 in the manner of a duplex triode. The tube I includes a cathode 4, a grid 5 and an anode 6, while the tube 2 is provided with a cathode 1, agrid 8 and an anode Ill. The anode H] of the tube 2 is connected to the grid 5 of the tube l through a coupling condenser ll. Similarly, the anode 6 of the tube l' is connected to the grid 8 of the tube 2 through a coupling condenser l2. A variable grid leak resistor l3 connects the grid 5 to ground. The cathode 4 is connected to ground through a lead It and the cathode l isconnected to ground through a cathode resistor l5.

The anodes 6 and H] are supplied with a potential from the positive terminal of a battery connected to a lead It which is positive with respect to ground. A resistor I'l is arranged between the lead It and a lead [8 which in turn is connected through resistors 20 and 2|, respectively, to the anodes I and B. A blocking condenser 22 connected between the lead I8 and ground bypasses to ground alternating current which may be present in the lead I8.

The input signal is impressed on the grid of the tube I through a couplinglcondenser 23. The output signal is developed across'the cathode resistor I5 and may be obtained through the lead 25.

Referring now to the operation of the multivibrator illustrated in Fig. 1,-assumetne-e c1e er operation to start at the instant thetube .2.has just been rendered conductin Atthis instant space current begins to flow from :th'e'positive pole of the battery through the space discharge path of the tube 2. This causesthepotential'of the anode I0 to be depressed by reason .of :the voltage drop across the anode resistor 20. The impression of the depressed anodeepotential by means of the .coupling condenser II upon the control grid -5 of the tube .bia'se's 'thistube be- "yond-cutofif so that the conduction of space currenttherein is terminated. Accordingly, the tube :2 now conducts space curren't while the tube I is-non-conducting.

The-grid voltage tube 2 in this-state must be above-cutofi" value but be somewhat "below cathode potential .s'incei f the grid .becomes more positive than cathodeiit w'ill immediately collect electrons which will reduce l it's voltage.

The charge of theeoupun condenser H is gradually dissipated through Jthe -grifd leak resistor I 3, and vtherebythe controlgrid voltage of the tube I is gradually increased. 'Ultimatel'y, this voltage reaches I the space .fcur'reri-t cutoff value, andconduotion -.agaii1.i's 'Yini'tiated in 'th'etub'e I. Immediately the potential of the anode 6 is depressed by :reason of the space i current "flow through the anode ,res'is'torfz'I; 'Theiinpr'e'ssion of this depressed anode .voltage by means .(if the coupling =condenser I2 upon the control grid '8 of the .tube 12 depresses 'in turn .the control grid voltage of the tube 12 .ibelow its space current cu-tofi walue, The termination o'ffthespace current in the tube '2 causes anmcreasesf the potential ofthe-anodelfl .asthereds no longer a voltage drop across the .anoderesistoififli.' This, in turn, increases .the rpotential of the control grid 15 of the-tube 'I impressed-throughithe coupling cOndenser I l, and thus the "current "How 'in the tube I is increasedtstilltfurther, ,Kt fthis instant the tube I conductsIs'pace current .whil'eithe tube "2 is non-conducting.

"However, in .contra'dis tinction, to the typical -multivibratorv operatingecyele thenegative voltage impressed-upon thegrid .18 of the tube 2 can not be removed in view of theffat that the grid 18 does not have a grid kleak resistor. Accordingly, some outside .control must lbef-introducedlfor ter- .-minatin the spacecurrent Jfiowing. in the ftub'e 'I In accordancewithothe presentfi nvention this is effected through {the condenser 1'23; vThe signal impressed upon the grid 5 ,.preferably (includes negative impulses-recurring at the iuridain'ental .irequency of the .input signal. .At this ypoin't of the operating cycle .a negative impulse 'of the input .signal is -.now.,impressed upon the .g'iid 5, biasing it beyond cutoff so that Ithe conduction of space current inthetube l listerminate'd. 'This causes an increase of the potential .of the anode 6 which removes through the coupling condenser t2 the charge onagrid 8. lInthi-s"wayspacecurrent begins again. to I'fiow through the tube '2.

The time constant of the external grid ii cli s of the tube I is determined by the values of the coupling condenser II and the grid leak resistor I3 which, as shown in the drawing, is variable.

On the other hand, the grid circuit of tube 2 has a substantially infinite time constant except when tube 2 is conducting and there is grid current flow therein because the grid ahasno grid leak resistor and,- accordingly, any charge impressed upon the coupling condenser I2 can not be dissipated to ground except only through tube 2. The value of the time constant of the tube I determines the point during the operating cycle of .the multivibrator when the tube I begins to conduct space current again. The point when the conduction of space current in tube I is ter- ,minated, is determined by the arrival by the negative impulse of the input signal impressed zup'onlthe grid 5. Hence, for a given fundamental frequency of the input signal the value of the time constant of the tube I determinesfthalength of time during eachroperating.cycleduringwhich the tube --I does not conduct .space current. .-0n the other hand, as explained previously, the tube 2 conducts space current substantiallyrdu-ring those periods when the tube I is .rendered -nonconducting and vice-versa .By a-djusting,.-.the

variable. grid leak resistor 13 the;. time constant of the first tube can Foe-vaiid-yaThis in turn chan'ges'the length of time in each operatingtcyoie during'whichthetube I 'doe's'not conductspeoe current and, therefore, also controls the 'flength of "time during which the tube 2 conducts spece current. Thus, the width or th'e output -pulses which are derived fromthe tube i canbead juste'd by means o'f'th'e variable gr-id 1eak=resistor 13 The output signal is developed across metathode resistor l-5, and the outputsignal may be obtained from-the leajd' 25. Analysis-of thisoutput signal proves it to be a sharper square wave form than any obtained heretofore; The grid "current as well "as the anode current of 'theftube 2 flowsthrough the cathoderesistor I5 whichiniay account for the sharper square wave form obtained with the mu'ltivibrator'illustrated in"Fig. '1.

While it will be understood thatthe' circuit specifications of the multivibrato'r' shownrinll'lg. 1.may vary according -to thedes'ign ofany particular application, the'follow'ing circuit specifications .for a multivibratorare included, by way of example only,.suitable Ffor apulse trequ'ency {of .the order of 40 kiloc-ycles andnusing .a duplex triode of the GFSG-ty-pe:

Amplitude of the negative 'driv'ing pulses z fio'volts :Positive pot'ential :iof the battery I250fto'300'vo1ts Condenser I2 .002 microfarad fcondenser I I. 100 nucro=microfarads Condenser 122 .25 microfarad icond'ens'er :"23 mic'ro microfarads Resistor 15. I-LOOObhms Resistor 2G 10,000 ohms sR-es'istor .24 1,000.ohms sResistor 'II.- 10,000'ohms Variabler-esistorI? 100,000-ohms.

Referring now to Fig. '2, in which -like components are designated by the same reference numerals "as were used in Fig; 1, it 'willbesee'n that the multivibr-ator circuit 'is substantially identical with the one shownLin li'ig. 1. jFig.l'2 diners from Fig. "1 onlyby a'va'riable 'catho'dejr'esistor '30 arranged betweenthe cathode f4, ground. It has been 'foun'd "experimentallyih'at the variable cathode resistor makes the multi- .vibrator circuit of Fig. 2 self-oscillating.

The frequency of self-oscillation has been found to depend on the value of resistor 30. Asis well known such a free running oscillator can be synchronized by pulses occurring at approximately By using the same specifications, as given by .way of example in connectionwith Fig; 1, the

multivibrator illustrated in Fig. 2 can .bemade to operate satisfactorily. Theresistor 30 should be variable between about 5,000 to 10,000 oh-ms.

While there has been described what are. atpresent considered the preferred embodiments ofthe invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from theinvention, and it is, therefore, aimed in the appended claims to cover all such changes and. modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A square wave generator comprising a multivibrator including a first electric'dischar'ge device and a second electric discharge device, each having a cathode, a grid and an anode, condensers for coupling the anode of each of saiddevices to the grid of the other device, meansfor supplying a potential to said anodes thatis'positive with respect to ground, a grid leak resistor for connecting the grid of said first device to ground, another resistor for connecting thecathode of said second device to ground, said first device having a predetermined time constant determined by the condenser coupling the grid of said first device tojthe anode of said second device and said grid leak-resistor, the grid of said second device being externally insulated from its cathode so that the coupling circuit -of said second device has' a nominally infinite time constant, means for supplying an input-signal to said multivibrator, and an output circuit coupled to said second device. 7

*2. A square wave generator comprising a multivibrator including a first electric discharge desaid first device, and an output circuit coupled to saidsecond device.

3. A square wave generator comprising a multivibrator including a first thermionictube and a second thermionic tube, each having a cathode, a grid and ananode, condensersfor coupling'the anode of each of said tubes to the gridof the other tube, resistors connected to said anodes, means for supplying through said resistors a potential to said anodes that is positive with respect to ground,a variable grid leak resistor for con;- necting the grid of said first tube to ground, the cathode of said first tube being connected to ground, another resistor for connecting the oathode of said second tube to ground, said first tube having a predetermined time constant determined by the condenser coupling the grid of said first tube to the anode of said second tube and said variable grid leak resistor, the grid of said second tube being externally insulated from its cathode so thatthe coupling circuit of said second device has a nominally infinite time constant, means for supplying a negative impulse input signal to the grid of said first tube,-and an output circuit connected across the cathode resistor of saidsecond tube. l f

4; A square wave generator comprising a multivibrator including a first thermionic tube and a second thermionic tube, each having a cathode, a grid and an anode, condensers for coupling the anode of each of said tubes to the grid of the other tube, resistors connected to said anodes, means for supplying through said resistors a potential to said anodes that is positive with respect to ground, a variable grid leak resistor for connecting the grid of said first tube to ground, the

stant, means for supplying a negative impulse input signal recurring at :a fundamental frequency to the grid of said first tube to control the termination of the current conducting period of said first tube, and an output circuit connected across the cathode resistor of said second tube for deriving a square wave output signal at said fundavice and a second electric discharge device,- each having a cathode, a gride and an anode, condens- ,sa'id first device to the anode of said second device and said grid leak resistor, the grid of said second device being externally insulated from its cathode so that the coupling circuit of-said second device has a nominally "infinite time constant, means for supplyinga negative impulse input signal' to mental frequency, said variable grid leak resistor controlling the duration of the current conducting period of said second tube and thereby the width of said square wave output signal.

5. A square wave generator comprising a multivibrator including a first electric discharge deviceand a second electric discharge device, each having a cathode, a grid and an .anode, condensers for coupling the anode of each of saiddevices to thegrid of the other device, means for supplying a potential to said anodes that is positive with respect to ground, a grid leak resistor for connecting the grid of said first device to ground, resi-stors for connecting each of said cathodes individually to ground, said first device having a predetermined time constant determined by the condenser coupling the grid of said first device to the anode of said second device and said grid leak resistor, the grid of said second device-being externally insulated from its cathode so that the coupling circuit of said second device has'a nominally infinite time constant, means for supplying vice having a nominally infinite time constant, third impedance means for conductively connecting the cathode of said second device to ground, means for supplying an input signal to said multivibrator, and an output circuit coupled to said second device.

12. A square wave generator comprising a multivibrator including a first electric discharge device and a second electric discharge device, each of said devices having a cathode, a grid and an anode, condensers for coupling the anode of each 10 of said devices having a cathode, a grid and an anode, impedance means for coupling the anode of each of said devices to the grid of the other device, means for supplying a potential to said anodes that is positive with respect to ground, a

grid leak resistor "for connecting the grid of said first deviceto ground and cooperating with said impedance means to impart to said first device a finite time constanufmeans for completing. the

cathode circuit of said first device to ground; im-

, pedance means coupled to said second device havof said devices to the grid of the other device,

means for supplying a potential to said anodes that is positive with respect to ground, a grid leak resistor for connecting the grid of said first device to ground and cooperating with said condensers to impart to said first device a finite time constant, means for completing the cathode cir- 'ing a nom inaily infinite time constant, a resistor for connecting the cathode of said second device to ground and deriving a square wave output signal from said second'device, and means for supplying an input signal to said multivibrator:

JOSEPH D. SCHANTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,922,650 WilIoughby Aug. 15, 1933 2,392,114 Bartelinlr Jan. 1, 1946 2,406,096 Morrison Aug. 20, 1946 2,416,201

Nagel et a1 Feb. 18, 1947 

